Mattress spring core construction over the years has been a continuously improving art with advancements in materials and machine technology. A well known form of spring core construction is known as a Marshall spring construction wherein metal coil springs are encapsulated in individual pockets of fabric and formed as elongate or continuous strings of pocketed coil springs. In an earlier form, these strings of coil springs were manufactured by folding an elongate piece of fabric in half lengthwise to form two plies of fabric and stitching transverse and longitudinal seams to join the plies of fabric to define pockets within which the springs were enveloped.
More recently, improvements in spring core constructions have involved the use of fabrics which are thermally or ultrasonically weldable to themselves. By using such welding techniques, these fabrics have been advantageously used to create strings of individually pocketed coil springs wherein transverse and longitudinal welds, instead of stitching, are used to form the pockets encapsulating the springs. A fabric which has been used and proven to ultrasonically weld to itself is a non-woven polypropylene fabric which is extremely permeable to airflow. In other words, air may freely flow through the non-woven polypropylene fabric.
Once strings of pocketed springs are constructed, they may be assembled to form a spring core construction for a mattress, cushion or the like by a variety of methods. For example, multiple or continuous strings may be arranged in a row pattern corresponding to the desired size and shape of a mattress or the like, and adjacent rows of strings may be interconnected by a variety of methods. The result is a unitary assembly of pocketed coil springs serving as a complete spring core assembly.
Spring cores may be generally covered on the top and often on the bottom by pads of resilient foam as, for example, a pad of urethane or latex/urethane mix of foamed material. Within the last several years, more expensive cushions or mattresses have had the spring cores covered by a visco-elastic foam pad, which is slow-acting or latex foam, which is faster-acting, than visco-elastic foam. That is, the visco-elastic foam pad is slow to compress under load and slow to recover to its original height when the load is removed from the visco-elastic foam pad. These visco-elastic pads, as well as the latex pads, impart a so-called luxury feel to the mattress or cushion. These pads also, because of their open cell structure, retain heat and are slow to dissipate body heat when a person sits or lies atop such a foam pad-containing cushion or mattress.
Individually pocketed spring cores have been made with fabric material semi-impermeable to airflow through the fabric material, as disclosed in U.S. Pat. No. 7,636,972, which is fully incorporated herein. Such fabric may comprise a non-woven polypropylene base layer having one or more layers of material sprayed or coated thereon to retard the rate of compression and expansion of the pocketed springs. The permeability of the coated fabric is retarded such that when a load is placed on a pocketed spring assembly made with such semi-impermeable fabric, the rate at which the pocketed spring assembly compresses is slowed. Similarly, when a load is removed from the pocketed spring assembly, the rate of expansion of the pocketed springs is slowed, thus imparting a luxury feel to the pocketed spring assembly.
Making a pocketed spring assembly with coated semi-impermeable fabric may be challenging in an industrial setting. Coated semi-impermeable fabric contains layers which may not be conducive to ultrasonic welding which may make weld consistency challenging.
Another drawback of a pocketed spring assembly made from coated semi-impermeable fabric is that the fabric of the pocket may create “noise”, as the sound is named in the industry. Such noise may be created by the fabric expanding upon removal of the load due to the coil spring's upwardly directed force on the fabric.
It is therefore an objective of this invention to provide a pocketed spring assembly which is made with fabric impervious to airflow through the fabric, but may allow air to enter and exit the pockets via gaps in the seams of the pockets.
It is therefore an objective of this invention to provide a fabric for a pocketed spring assembly which is impervious to airflow through the fabric, but may be secured to itself consistently with segmented seams.
It is another objective of this invention to provide a method of making a fabric for a pocketed spring assembly which ultrasonically welds to itself, impervious to airflow through the fabric, and quiet.